1. Field of the Invention
The present invention relates to improvements in a surface contour measuring tracer wherein a measuring element supported movably in directions of three axes perpendicularly intersecting one another through an X-, Y- and Z-sliders mounted on a base is moved on a surface of a work in sliding contact therewith to thereby detect a surface contour of the work as an electric signal.
2. Description of the Related Art
There have heretofore been known such contact type surface contour measuring apparatuses, in each of which a surface contour measuring tracer is mounted on a CNC coordinate measuring instrument or the like, and a measuring element (probe) of this tracer is moved on a surface of a work in sliding contact therewith while a surface contour of the work (an object to be measured) is continuously followed and measured.
Heretofore, in general, the surface contour measuring tracer of this type has been of such an arrangement that an X-slider, Y-slider and Z-slider which are movable in directions of respective axes are successively mounted on a base fixedly secured to a CNC coordinate measuring instrument or the like, a measuring element is fixed to one of these sliders, the measuring element is made to be movable in directions of three axes perpendicularly intersecting one another with respect to the base, and, a neutral position holding means is provided for restoring the measuring element to a neutral position with respect to the base, i.e. origins of X, Y and Z when the measuring element is in non-contact with the work. For example, in a surface contour measuring tracer as described in U.S. Pat. No. 3,869,799, respective sliders are carried by parallel springs, movements of the respective sliders in the directions of respective axes are permitted by the parallel springs, measuring forces of the sliders are secured, and further, a neutral position holding means is provided for restoring the measuring element to origins. However, such disadvantages have been presented that an error in the direction of Z-axis generated due to a dispersion in a positional accuracy, non-linear characteristics and degree of deformation is great at the time of assembling and fixing the parallel springs, whereby the directional properties are reflected in the measured values. In contrast thereto, as an improved surface contour measuring tracer wherein stabilized measuring forces (contact forces) or moving properties are provided in the directions of X-, Y- and Z-axes, the measuring element can be easily restored to the neutral position and the following properties to the surface of the work are improved, in Japanese Patent Unexamined Publication No. 61-50007, there is proposed one wherein the parallel springs are removed, the respective sliders are successively and slidably supported in the directions perpendicularly intersecting one another, and the neutral position holding means is formed by return springs, thus obviating the above-described disadvantages.
However, with the conventional surface contour measuring tracer, and particularly, even with the latter improved tracer, requirements at present such as rendering the tracer compact in size and light in weight and performing measuring at high accuracy cannot be satisfied.
More specifically, the sliders are successively assembled slidably in the directions of the axes perpendicularly intersecting one another, that is, a so-called three-stage pile-up system is adopted, whereby the tracer becomes large-sized, thus presenting such disadvantages that, not only a heavy load is imposed on the contact type surface contour measuring apparatus, but also the effective measuring space is reduced to deteriorate the measuring efficiency, and moreover, the work cannot but be limited to a small one.
The neutral position holding means is interposed between the sliders or provided at the outer peripheral portions of the sliders, so that the tracer is further large-sized.
Rendering the surface contour measuring tracer large in size poses the problem of that the performance of the tracer itself cannot be improved beyond a predetermined level. In short, with the construction of the above-described three-stage pile-up system, loads of the sliders other than that provided at the bottom stage are increased, whereby differences occur in the moving properties between the sliders, so that the directional properties in the measured values become large. Biasing forces for the neutral position holding means should be set at large values, so that such problems are presented that it is difficult to reduce the measuring forces, measuring errors easily occur, and it is impossible to measure the contour of plastic product and the like. In addition, the finishing accuracy of parts should be high-leveled for the purpose of smoothly and slidably guiding and connecting the sliders to one another, and excessive amount of labor and excessive time are spent for assembling and adjusting, thus resulting in poor economics. Further, in general, the neutral position holding means is constituted by an origin restoring means in a horizontal plane and an origin restoring means in a vertical plane, whereby both means become large-sized in construction, so that both means are different in construction, load and biasing force from each other, and accordingly, dispersions in directional properties occur, thereby inducing complicated problem such as natural vibrations.